1. Field of the Invention
The invention relates generally to an electrically powered vehicle, such as an electric vehicle (EV), a hybrid electric vehicle (HEV) or a fuel cell vehicle (FCV). More specifically, the invention relates to a strategy to diagnose a potential deviation in operating characteristics of an electric motor. The present invention can determine two independent electric motor torque estimates using a plurality of current transducers and optionally a shaft position sensor for the traction motor.
2. Background Art
The invention may be used in a hybrid electric vehicle of the type schematically shown in FIG. 1 of co-pending application Ser. No. 09/683,026, filed Nov. 9, 2001, which issued on Feb. 10, 2004 as U.S. Pat. No. 6,688,411; in FIG. 1 of co-pending application Ser. No. 09/712,436, filed Nov. 14, 2000, which issued on Dec. 16, 2003 as U.S. Pat. No. 6,664,651; as well as in co-pending applications Ser. No. 10/063,345, filed Apr. 12, 2002, now abandoned; and Ser. No. 09/966,612, filed Oct. 1, 2001, which issued on May 11, 2004 as U.S. Pat. No. 6,735,502. Each of these co-pending applications is assigned to the Assignee of the present invention.
The need to reduce fossil fuel consumption and emissions in automobiles and other vehicles predominately powered by internal combustion engines (ICEs) is well known. Vehicles powered by electric motors attempt to address these needs. Another alternative solution is to combine a smaller ICE with electric motors into one vehicle. Such vehicles combine the advantages of an ICE vehicle and an electric vehicle and are typically called hybrid electric vehicles (HEVs). See generally, U.S. Pat. No. 5,343,970 to Severinsky.
The HEV is described in a variety of configurations. Many HEV patents disclose systems in which an operator is required to select between electric motor and internal combustion engine operation. In other configurations, the electric motor drives one set of wheels and the ICE drives a different set.
Other configurations include, for example, a series hybrid electric vehicle (SHEV) configuration. A series hybrid vehicle has an engine (typically an ICE) connected to an electric motor/generator. The generator, in turn, provides electricity to a battery and another motor, called a traction motor. In the SHEV, the traction motor can function as the sole source of wheel torque. There is no direct mechanical connection between the engine and the drive wheels. A parallel hybrid electrical vehicle (PHEV) configuration has an engine (typically an ICE) and an electric motor that work together in varying degrees to provide the necessary wheel torque to drive the vehicle. Additionally, in the PHEV configuration, the motor can be used as a generator to charge the battery using power produced by the ICE.
A parallel/series hybrid electric vehicle (PSHEV) has characteristics of both PHEV and SHEV configurations. It sometimes is referred to as a “split-power” configuration. In one of several types of PSHEV configurations, the ICE is mechanically coupled to two electric motors in a planetary gear-set transaxle. A first electric motor, the motor/generator, is connected to a sun gear. The ICE is connected to a planetary gear carrier. A second electric motor, a traction motor, is connected to a ring (output) gear via additional gearing in a transaxle. Engine torque can power the generator to charge the battery. The generator can also contribute to the necessary wheel (output shaft) torque. The traction motor is used to contribute wheel torque and to recover braking energy to charge the battery. In this configuration, the generator can selectively provide a reaction torque that may be used to control engine speed. In fact, the engine, motor/generator and traction motor can provide a continuous variable transmission (CVT) effect. Further, the HEV presents an opportunity to better control engine idle speed, compared to conventional vehicles, by using the generator to control engine speed.
The desirability of combining an ICE with electric motors is clear. There is potential for reducing vehicle fuel consumption and emissions with no appreciable loss of vehicle performance or driveability. The HEV allows the use of smaller engines, regenerative braking, electric boost, and even operation of the vehicle with the engine shut down.
One such area of development for optimizing potential benefits of a hybrid electric vehicle involves calculating torque estimates delivered by an electric motor or motors. An effective and successful HEV design (or any vehicle powertrain propelled by electric motors and optionally capturing regenerative braking energy) requires reliable operation that can be improved through careful diagnosis of electric motor operation. Thus there is a need for a strategy to effectively detect potential discrepancies in electrical operating characteristics in an electric motor propelled vehicle's electrical components and sub-systems.
Previous efforts have used rotor position sensors or estimates as part of the control strategy for an electric motor. For example, Jones et al. (U.S. Pat. No. 6,211,633) disclose an apparatus for detecting an operating condition of a machine by synchronizing sampling instants with the machine condition so that reliability data are obtained. The operating condition may be the position of the rotor, in which case estimates of the rotor position and rotor velocity at each of the sampling instants are developed.
Lyons et al. (U.S. Pat. No. 5,864,217) disclose an apparatus and method for estimating rotor position and commutating a switched reluctance motor (SRM), using both a flux/current SRM angle estimator and a toothed wheel generating a magnetic pickup. Phase errors can be compensated by adjusting the angle input to the commutator as a function of estimated speed. Alternately, the flux/current SRM angle estimator can be run in background mode to tune the toothed wheel interrupt angle signal at different speeds.
Drager et al. (U.S. Pat. No. 5,867,004) disclose a control for operating an inverter coupled to a switched reluctance machine that includes a relative angle estimation circuit for estimating rotor angle for a phase in the switched reluctance machine.
Lyons et al. (U.S. Pat. No. 5,107,195) disclose a method and apparatus for indirectly determining rotor position in a switched reluctance motor that is based on a flux/current model of the machine, which model includes multi-phase saturation, leakage, and mutual coupling effects.
Lastly, Acarnley (U.S. Pat. No. 6,005,364) discloses a motor monitoring and control circuit that calculates a value parameter for a position of the motor at given instants. The same parameter (which may be position or speed of a rotor) is then measured at subsequent instants. These values are used to compute a future value of the parameter.
The use of two independent torque estimates to diagnose a potential deviation in the operating characteristics of the electric motor in an electric motor propelled vehicle is unknown in the prior art.